1. Field of the Invention
The present invention relates to a method and device for producing short fibers by converting thermoplastics into short fibers through the use of centrifugal force.
The short fibers produced in accordance with the present invention are intended for use in forming fused molded products as set forth in applicant""s prior application Ser. No. 09/331,199, hereby incorporated in its entirety by reference.
2. Prior Art
Conventionally, extrusion molding is generally used as a processing technique for obtaining fiber wool, and mechanical and forceful dispersion or fragmentation of plastic particles has been attained by a kneading screw built in an extruder or the like, obtaining fiber wool by eluting a plastic through a tip nozzle under the extrusion pressure of the screw. However, in the case where such melt spinning method is used to apply melt kneading to a variety of plastics which are in incompatible relationship, forceful shearing of dispersed particle and fragmentation of polymer are repeated by the screw, so that the polymer obtained by the kneading of incompatible polymers is a low polymer, which has failed to provide extensible fiber wool.
Japanese Patent Kokai Publication Sho 59-179811, Japanese Patent Kokai Publication Hei 6-322606, etc, propose fiberizing devices utilizing centrifugal force, but any of these devices is destined for fiberizing thermosetting resins, such as phenol resin. That is, such device is a fiberizing device for obtaining a catalytic reaction by rotating a phenol solution, with emphasis placed on catalytic reactions in solidification and cooling action after delivery.
Conventionally, the fiberization technique for obtaining fiber wool from thermoplastic has generally been extrusion spinning. Extrusion spinning comprises the steps of melting a plastic by a kneading screw built in a extruder in combination with heat radiation from the outside of the cylinder, and mechanically and forcefully extruding the plastic for melt-spinning through a delivery nozzle, thereby stably providing plastic fibers.
With such mechanical and forceful melt spinning method, however, when a variety of plastics consisting of composite raw materials or the like are simultaneously melted, this results in the built-in screw mechanically and forcefully applying dispersion or shearing, during which time individually polymers are subjected to repetitive fragmentation and mixing, so that the resulting plastic fiber is a plastic fiber composed of embrittled low polymers; it has been impossible to spin a plastic fiber which possesses extensibility and viscoelastic function, which are originally required and which are characteristic of high polymers.
As for centrifugal spinning devices, Japanese Patent Kokai Publication Sho 62-104908, Japanese Patent Kokai Publication Sho 62-17052, Japanese patent Kokai Publication 2000-50511, etc. disclose fiberizing devices which utilizes centrifugal force. However, any of the centrifugal spinning device is a rotational centrifugal spinning machine or the like additionally using glass or carbonaceous pitch fibers or an extruder, and any other disclosed centrifugal spinning devices are based on the precondition that the centrifugal device be fed after preprocessing is effected for molten or liquidized raw material; it has been impossible to feed crushed pieces of plastic or a composite raw material directly as a raw material. As a trial, a composite raw material was charged into an existing centrifugal spinning device, and the plastic was melted and gelled by the furnished heater or the like and then delivered for spinning plastic fibers; it was found that under the action of heat dissipation from the surrounding heat such as the heat from the heater installed in a rotational spinning dish, the polymers were subjected to the influence of heat history in the melting, shaping and solidifying processes, so that a phenomenon of deterioration such as carbonization or oxidation occurred. Therefore, the delivered plastic was spun into an embrittled fiber resembling a needle or bar, failing to attain the spinning of plastic fiber.
Along with development of new commodities, composition of plastic raw materials is under way and when these composited plastic products are once disposed of as waste, separation or classification of plastic raw materials become very difficult.
For example, in the case where a composite plastic consisting of 50:50 of crystalline plastic PP (polypropylene) and noncrystalline plastic PVC (polyvinyl chloride) is crushed and subjected as a trial to melt-spinning by a mechanical kneader (2-axis extruder), the individual polymers were repetitively dispersed and bonded by the screw built in the kneader, during which time the polymers of PP and the PVC react with each other, leading to a decrease in molecular weight, failing to provide a fiber wood which possesses extensibility. Therefore, perfect separation or classification to be attained as by finding a melt spinning method for PP alone after perfect separation of plastic have heretofore been considered to be the minimum processing condition for reclamation of waste plastic.
The inventor has found that pre-application of a process for a short fiber possessing extensibility is effective for reclamation of waste plastics, and on the basis of this finding, it is a technical problem to provide a short fiber wool possessing extensibility by conversion of individual plastics by applying a process to a variety of waste plastics in their mixed state without separation or classification even in the case of a waste of different kinds of plastics or composited plastic products of incompatible system.
Plastic wastes exist in a state in which varieties including PVC (polyvinyl chloride), PE (polyethylene), and PET (polyethylene terephthalate) are mixed. To proceed plastic recycle for these plastic wastes, according to the conventional recycle processing method, after plastic raw materials have once been identified, carefully selected raw materials alone are melted and then molded; thus, it has been considered difficult to process a variety of mixed plastic raw materials to provide recycled products possessing physical strength. With the conventional melt molding method, when it is desired to obtain a recycled article from PVC/PE mixed resin having PE, which is a different resin, incorporated therein with PVC used as a matrix, thermal strain, peeling, cracking or the like occurs in the PVC/PE interface; it has been quite impossible to obtain a product having values and physical strength.
The present invention is intended to provide a short fiber producing device wherein when melt molding is applied to a variety of mixed plastic raw materials for the purpose of effective utilization of resources, the polymer cohesive energy which is a cause of thermal strain, peeling or cracking occurring in recycled products is suppressed by melting the plastics in advance and finding molecular arrangement, thereby forming a single fiber composed of chained high polymer, and spinning plastic fibers possessing viscoelasticity and extensibility.
The invention provides short fiber production for obtaining plastic fibers possessing viscoelasticity and extensibility by using as a raw material a plastic composite raw material in the form of a mixture of a variety of kinds, such as PP (polypropylene), PE (polyethylene) and PET (polyethylene terephthalate). If the conventional melt spinning method, centrifugal spinning method or the like is used to try spinning on the basis of a composite material consisting of variety of kinds, the resulting plastic fibers are embrittled or deteriorated fibers resembling a needle or bar, failing to provide a plastic fiber possessing viscoelasticity and extensibility which are characteristic of plastic. The reasons and causes thereof have been investigated and the following main causes have been found.
(1) For a mixture of molten composite raw materials, when fragmentation and dispersion of polymer particles are simultaneously effected, the resulting plastic fiber changes into an embrittled fiber like a bar.
(2) If, for the melting process, an evolution from melting to shaping and then to solidifying is allowed to take a longer time than is necessary, the resulting plastic fiber changes into a fiber deteriorated like charcoal under the influence of heat history.
(3) Unless the cohesive energy of each polymer is suppressed for a melt mixture of composite raw materials, it is impossible to suppress the influence of thermal strain or phase separation on the mixture.
In the present invention, it has been found that quickly finding the molecular arrangement of each polymer from the raw material state of solids in the form of crushed plastic pieces, composite raw material or the like with respect to the cause of embrittlement or deterioration said to be due to plastic composite raw material and then effecting melt spinning makes it possible to spin a plastic fiber possessing viscoelasticity and extensibility.
Accordingly, the present invention is characterized by employing high frequency induction heating to accurately control and manage the melting temperature of plastic and additionally using centrifugal force concomitant with high speed rotation to quickly find the molecular arrangement of each polymer, thereby spinning a fiber possessing viscoelasticity.
In the present invention, the raw material receiving chamber for receiving a raw material is in the form of a rotor, and an inductor is disposed in the vicinity of the rotor. Passing a high frequency electric current through the inductor generates alternating magnetic flux in the rotor itself. On this occasion, by changing the resistance to and the frequency of the high frequency current flowing through the inductor, etc. the generation of Joule heat concomitant with the generation of the alternating magnetic flux is found from the surface of the rotor without contacting the latter, and the heating action of the rotor is locally obtained.
Unlike the outside heating action provided with heat dissipation from the outside, such as heater heat or hot wind disclosed in Japanese Patent Kokai Publication Sho 62-238807, Japanese Patent Kokai Publication Sho 62-104908, Japanese patent Kokai Publication 2000-50511, etc., this makes it possible to construct the rotor itself as a heat dissipation body. Generating alternating magnetic flux and applying heat generated by electromagnetic induction to a resin reservoir tank in the form of a local portion minimizes the influence of heat history. Quick spinning by centrifugal force concomitant with high speed rotation makes it possible to find the molecular arrangement of each polymer used as a composite raw material, thus making possible the melt spinning of a short plastic fiber possessing both extensibility and viscoelasticity at the same time.
According to an embodiment of the invention, a short fiber producing device comprises a rotor having a raw material receiving chamber having an outlet disposed in the outer periphery, it being arranged that the centrifugal force concomitant with the rotation of said rotor causes a fluidized body of plastic to be delivered from said outlet to provide short fibers, wherein a resin reservoir tank is provided inside said outlet. When melting and kneading are to be effected by crushing or by polymer dispersion in the conventional processing method, it has been impossible to treat the problem of polymer cohesive energy produced in the molded body. In the present invention, however, heated and melted plastic is fiberized by utilizing centrifugal force, whereby even for incompatible plastics in their mixed molten state, individual polymer molecular arrangements are found, so as to provide a short fiber of chained high polymer. Most of the plastic products which are wastes are composited plastic products made of incompatible plastic raw materials; thus, for recycling of plastics, melting of individual plastics must be effected in the mixed state of different kinds of these incompatible plastics, and attainment of this makes it necessary to secure an arrangement for a fiber possessing extensibility without involving a reaction between plastics which leads to lower molecular weight. To this end, rather than causing polymer dispersion and plastic particle breakage to occur as by mechanical kneading, a heat source is obtained in the outside to lead plastics in their high molecular state to a molten state, while subjecting the molten polymers themselves to a pressing force corresponding to the screw extrusion pressure by using centrifugal force concomitant with rotation of the rotor and change (increase) in flow pressure due to a resin reservoir tank, whereby a short fiber possessing extensibility can be obtained.
The cross sectional area of the resin reservoir tank may advantageously decrease as the outer diameter side of the rotor is approached. The decrease in cross sectional area means an increase in delivery pressure. For example, the resin reservoir tank may be a side wall positioned on the advance side as seen in the direction of rotation of the rotor and a side wall positioned on the delay side, and the side walls on the advance and delay sides form an angle therebetween. In this case, the side walls on the advance and delay sides may be symmetrical. Besides this, the side wall on the delay side may extend radially of the rotor and the side wall on the advance side forms an angle with respect to the side wall on the delay side. This arrangement ensures that the side wall on the delay side extending radially of the rotor acts as a pressure wall perpendicular to the direction of rotation, thus enhancing the pressure increasing effect. Further, in this case, since the side wall on the advance side is inclined with respect to the direction of rotation, it performs the role of introducing the molten plastic into the resin reservoir tank. The angle of inclination of the side wall on the advance side can be referred to as plastic inflow angle.
Thus, the cross sectional area or volume of the resin reservoir tank is sharply decreased by the plastic inflow angle while storing the molten plastic once in the resin reservoir tank, resulting in the plastic flow pressure being amplified. Additionally, concentrating the centrifugal action of the rotor on the outlet makes it possible to find the arrangement of molecules with respect to the direction of flow of the plastic and to obtain a fiber further possessing extensibility by means of centrifugal force.
The cross sectional area of the raw material receiving chamber may advantageously decrease as the outer diameter side of the rotor is approached. In other words, the cross sectional shape may narrow toward the front as seen in the direction of flow of raw material plastic. The shape narrowing toward the front may be in the form of a taper or a gradient. Such arrangement amplifies the pressure on the raw material plastic as the outer diameter side, or the outlet, of the rotor is approached.
A heating device may be provided adjacent the rotor. This heating device heats and melts the raw material plastic in the raw material receiving chamber. The plastic heated and melted not by mechanical kneading but by an outside heat source flows, in the form of chained high polymer, into the resin reservoir tank under the action of centrifugal force without polymer dispersion. The heating device is disposed on the upper surface and/or the lower surface of the rotor. As for the heating device, electric type, infrared type, heat medium type and other suitable type heaters may be employed selectively or in combination. High frequency heating may be employed.
A plurality of temperature regions may be provided radially of the rotor, the temperature in each region being adjustable. This ensures that different kinds of plastics fed into the raw material receiving chamber melt in separate positions according to their melting points.
The rotor may be composed of separable upper and lower halves. Such arrangement facilitates not only the processing of the outlet and resin reservoir tank but also cleaning, maintenance and inspection thereof. For example, provision of a groove of semicircular cross section in the mating surface of each of the upper and lower halves forms an outlet in the form of a hole of circular cross section when the two are put together. Alternatively, it is possible to interpose an outer peripheral ring between the upper and lower halves and provide a delivery port in the outer peripheral ring. A delivery metal gadget having a delivery port may be removably attached to the outer peripheral ring. Further, the inner wall of the delivery port may be shaped to have a concave or convex cross section to suppress the flow of plastic.
The upper half of the rotor may be centrally provided with a hollow cylindrical portion for feeding raw material. This makes continuous feeding of raw material possible. For example, inserting the discharge port of a loading hopper or, if a heater, dryer or any other pre-processing device is installed, the discharge port thereof into the hollow cylindrical portion, makes it possible to feed raw material without stopping the rotation of the rotor.